Neutron EDM Experiment at the Paul Scherrer Institute Jacek Zejma on behalf of the nEDM collaboration SSP2012, Groningen Jacek Zejma Jagiellonian University Kraków
Motivation � � � � ∙ �̂ � � � � P � � � ∙ �̂ _ � + _ + � ~ 10 ��� T Non-zero nEDM value violates � � both P and T symmetries. ~ 10 ��� � � �������� R _ + _ + Motivation of neutron EDM measurements has been already presented in several interesting talks. 2 Jacek Zejma SSP2012, Groningen
Motivation First nEDM experimental estimation: E. M. Purcell and N. F. Ramsey (1950) d n < 3·10 − 18 e·cm First dedicated nEDM measurement: Smith, Purcell, Ramsey (1957) d n < 5 · 10 –20 e · cm Current experimental limitation: RAL-Sussex-ILL collaboration (2006) d n < 2.9·10 –26 e·cm. Problem of last experiments: Limited statistics d n =(+0 . 2 ± 1 . 5 ± 0 . 7)·10 -26 e·cm. 3 Jacek Zejma SSP2012, Groningen
Experiment at PSI General idea: • continuation of the successful Sussex/RAL/ILL experiment. • much more intense UCN source • better control of the systematics Paul Scherrer Institute: • new UCN source with intensity of above 1000 cm -3 (typical density at ILL is 10 cm -3 ). Bernard Lauss’s talk on Wednesday (17:20). 4 Jacek Zejma SSP2012, Groningen
Experiment at PSI Last result: d n < 2.9·10 –26 e·cm. Aim sensitivity of the experiment at Paul Scherrer Institute: • Intermediate : d n < 5 · 10 -27 e · cm (95% C.L.) • Finale : d n < 5 · 10 -28 e · cm (95% C.L.) d ≈ 0.7 µm if neutron is enlarged to the size of the Earth. 5 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Collaboration of 13 laboratories 51 scientists (including PhD students) 6 Jacek Zejma SSP2012, Groningen
Measurement principle Larmor precession of the neutron spin � � � � � � � � � ↑↑ � � � � ↑↑ , if � ↑↑ � . � � � � � � � � � � � ↑↓ � � � � ↑↓ , if � ↑↓ � . ∆� � 2 � � � � ↑↑ � � ↑↓ � 2 � � � � ↑↑ � � ↑↓ ω L � � ∆� � � � � � , if � � � ↑↑ � � ↑↓ and � ↑↑ � � ↑↓ . � � ~�� ��� ⟹ ∆� � ~� ∙ �� ��� . 7 Jacek Zejma SSP2012, Groningen
Measurement principle The Ramsey method of separated oscillating fields Sample of polarized neutrons with 1. constant � (1 μ T) i � (12 kV/cm) field. RF pulse with � �� � � � �� 30Hz� . Spin rotation by � � ⁄ to horizontal plane. 2. Free precession of neutron spin by 3. about 120 150 s. � ↑↑ � or � ↑↓ � . Second 2s long RF pulse. Rotation of 4. spin � � ⁄ to vertical if d n =0. Neutron polarization analysis. 5. 8 Jacek Zejma SSP2012, Groningen
Measurement principle The Ramsey method of separated oscillating fields Amount of registered C 1 neutrons with polarization equal +1 for E=0. x – working points � � � � � � � C 2 � � � � � Measurement accuracy: � � � � � P.G. Harris et al., PRL 82 (1999) 904 2��� � 9 Jacek Zejma SSP2012, Groningen
Measurement principle The Ramsey method of separated oscillating fields C 1 � � � � � � � C 2 � � � � � Measurement accuracy: � � � � � 2��� � 10 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI � System components: � � � � • Ultra-cold neutrons: 2��� � guides, precession chamber, valves. spin polarization and analysis. detection system. • Magnetic field: μ -metal shield. main and compensation (trim) coils. magnetometers to measure field and its gradients. • Electric field: power supply and electrodes. leakage current measurement. high-voltage resistant materials • Data acquisition system: sequence of steps in a measurement cycle. control of all subsystems. collection of data. 11 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Thermo-house with stabilized temperature. Apparatus with precession chamber 0.1°C Control room 1°C 12 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI 13 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI 14 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Switch connects UCN storage volume with • UCN source • Detection system • Pumping system • Pressure gauge 15 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI UCN detection system • 6 Li enriched scintillators n + 6 Li → 3 H + α UCN 110 µm 60 µm 6 Li depleted 3 H 6 Li 6 Li enriched 16 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Using nonmagnetic materials • Tests at PTB Berlin ∆ B pp ≈ 200 pT After demagnetization ∆ B pp ≈ 20 pT 17 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI 199 Hg co-magnetometer PM ~ 8 Hz B 0 ≈ 1 μ T polarization cell ¼ wave plate τ = 140 s linear polarizer Hg lamps HgO source 50 fT/100s 18 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI 199 Hg co-magnetometer 50 pT 19 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI 133 Cs magnetometers 4 HV-resistant Cs-mag 8 Cs-mag. Measurement of • field gradients, • rapid field changes. 100 fT/1s 20 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Magnetic field shielding • Passive: • 4 layers of μ -metal • Active: • Surrounding field compensation (6 coils) • 30 trim coils Field mapping. Longitudinal neutron spin relaxation T 1 = 3600 s, Transverse relaxation T 2 = 560 s. 21 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Mean � values of Hg atoms and UCNs in the precession chamber differ by ∆� ≈ 2.3 mm – this is a source of uncompensated field drifts: � � 1 � �� �� ∙ 1 ����� � � � � � � � ∙ ∆� � �� � �� Measurement of gradient: < 2.8 fT/cm What corresponds to systematic effect 2.5 ∙ 10 ��� e ·cm With CS magnetometers we can obtain accuracy ����� � 0.9 ∙ 10 ��� e ·cm � � � 22 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Towards n2EDM 1. Better magnetometry system. 2. Active magnetic shielding 3. Simultaneous measurement with E parallel and anti-parallel to B in the symmetric double-chamber system. 4. Simultaneous neutron “up” and “down” spin measurement. 23 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Summary 1. UCN source is ready for delivering neutrons. 2. All sub-systems tested and ready to work. • some improvements and tests are still being prepared. 3. Expected accuracy obtained in the measurement 2012-2013 � � � �… � 2 � 2� ∙ 10 ��� e ·cm. 4. Investigations regarding next step are in progress. 24 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Thank you 25 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Dedicated measurement for estimation of ∆� � � � � � � 1 � �� �� ∙ 1 � � ∙ ∆� � � �� �� ∆� = 2.3 ± 0.1 mm 26 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Status ( ⋅ 10 ‐ 27 ecm) Effect (Feb. 2012) Leakage Current 0.00 ± 0.05 Uncompensated B drift 2.9 ± 8.6 vxE UCN 0 ± 0.1 Electric Forces 0. ± 0.4 Hg EDM 0.02 ± 0.06 Hg Light Shift 0.00 ± 0.05 Quadrupole Difference 1.3 ± 2.4 Dipoles 0 ± 3 Total 4.2 ± 9.4 27 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Signals from a UCN detector 45 45 35 35 Č erenkov pulse Neutron pulse Signal (mV) Signal (mV) 25 25 15 15 5 5 0 100 200 300 400 500 -5 0 100 200 300 400 500 -5 Time (ns) Time (ns) 28 Jacek Zejma SSP2012, Groningen
nEDM experiment at PSI Long term magnetic field drifts measured with both Hg and Cs magnetometers 29 Jacek Zejma SSP2012, Groningen
Recommend
More recommend
